1. Technical Field
The present invention relates to a fuel injection control device for internal combustion engine and, more particularly, to an improvement in starting characteristic for starting the engine at a high temperature.
2. Background Art
FIG. 4 is a schematic view showing a fuel injection control device according to a prior art. In the drawing, reference numeral 1 is an engine, and numeral 3 is a fuel injection valve for injecting a fuel to the engine 1 and disposed on a pipe wall of an intake pipe 2. Injection quantity from the fuel injection valve 3 is arranged to be in proportion to the fuel injection time period. For that purpose, a pressure regulator 4 is disposed so that pressure difference between fuel pressure of the fuel injection valve 3 and pressure of the intake pipe (intake air pressure) may be set to a predetermined value. A fuel chamber of the pressure regulator 4 is communicated to a delivery pipe 5 from a fuel tank (not illustrated), and the pressure regulator 4 circulates the fuel to the fuel tank through a return pipe 6. A back pressure chamber is connected to a fuel pressure switching solenoid 8 through a pipe 7.
FIG. 5 is a diagram showing a relation between driving time t of the engine 1 and respective pressures (fuel pressures A, B, atmospheric pressure Pa, intake air pressure Pb). Under normal driving condition, the pressure regulator 4 uses the intake air pressure as a reference pressure of the back pressure chamber. Fuel pressure is adjusted to a value higher than the intake air pressure by a predetermined pressure P0. Accordingly, as shown in FIG. 5, when the intake air pressure Pb drops sharply at the time tst of starting the engine 1, the pressure regulator 4 starts its operation. As the result, the fuel is returned to the fuel tank through the return pipe 6, and the fuel pressure B in the delivery pipe 5 also drops sharply. Moreover, when starting the engine 1 under a high engine temperature including restart of the engine at a high temperature after a high speed driving, there is a possibility that vapors (air bubble) are generated in the delivery pipe 5, air fuel ratio is lean, and the start becomes difficult.
To overcome this difficulty, when it is detected that the engine 1 is under the condition of high temperature at the time of starting the engine 1, the reference pressure of the pressure regulator 4 is changed over from the intake air pressure Pb to the atmospheric pressure Pa by means of the fuel pressure switching solenoid 8, whereby the fuel pressure becomes higher than the atmospheric pressure Pa by the predetermined pressure P0. Thus, the fuel pressure is improved. As a result, the fuel deficiency due to the generation of the vapors is corrected by changing the fuel pressure in the delivery pipe 5 from the condition B to condition A, i.e., increasing the fuel pressure by xcex94P. In this manner, an appropriate quantity of fuel can be supplied to the fuel injection valve.
The fuel pressure switching solenoid 8 is connected to the intake pipe 2 through the pipe 7 and is open to the atmospheric air. When the fuel pressure switching solenoid 8 is off, the negative pressure Pb of the intake pipe 2 is applied to the back pressure chamber of the pressure regulator 4. On the other hand, when the fuel pressure switching solenoid 8 is on, the atmospheric pressure Pa is applied to the back pressure chamber of the pressure regulator. The on/off control of the fuel pressure switching solenoid 8 is performed by an ECU 12 on the basis of values measured by a water temperature sensor 9, an intake pipe pressure sensor 10 and an intake temperature sensor 11.
FIG. 6 is a flow chart showing the control by the ECU 12 of the conventional fuel injection control device. First, a water temperature WT is measured by the water temperature sensor 9, an intake air temperature AT is measured by the intake temperature sensor 11, and an intake air pressure Pb is measured by the intake pipe pressure sensor 10 (Step S101). Next, whether or not the engine 1 is in the mode representing a starting condition is judged (Step S102). When it is judged that the engine 1 is in the starting mode, the water temperature WT and the intake air temperature AT measured in the step S101 are renewed and stored as a starting water temperature WTst and a starting intake air temperature ATst, respectively (Step S103). When it is judged that the engine 1 is not in the starting mode, the operation advances to Step S104.
In Step S104, whether or not the water temperature WTst is higher than a predetermined value is judged. When it is judged that the water temperature WTst is higher than the predetermined value, then whether or not the intake air temperature ATst is higher than a predetermined value is judged (Step S105). When it is judged that the intake air temperature ATst is higher than the predetermined value,then whether or not the engine 1 is restarted within a predetermined time after the previous start is judged (Step S106). When it is judged that the engine 1 is restarted within the predetermined time, the fuel pressure switching solenoid 8 is turned on, and the atmospheric pressure Pa is introduced into the pressure regulator 4 (Step S107). On the other hand, when it is judged that the temperature WTst or ATst is lower than the predetermined value and the engine is restarted without the predetermined time in Steps S104 to S106, the fuel pressure switching solenoid 8 is turned off and the negative pressure Pb in the intake pipe is introduced into the pressure regulator 4 (Step S108).
As described above, after turning on/off the fuel pressure switching solenoid 8, a driving time period of the fuel injection valve 3 is calculated (Step S109). The driving time period Tinj is obtained from the following expression:
Tinj=Kinjxc3x97Pbxc3x97Ketc
where: Pb is the intake air pressure measured in Step S101, and Kinj is a coefficient for converting the intake air pressure Pb into the driving time period of the fuel injection valve 3.
The intake air pressure Pb is substantially in proportion to the intake air flow of the cylinder. Therefore, when the pressure difference between the intake air pressure acting on the fuel injection valve 3 and the fuel pressure is constant, the fuel injection quantity from the fuel injection valve 3 is in proportion to the driving time period thereof, and becomes a substantially constant ratio with respect to the intake air flow of the cylinder of the engine.
Ketc is a coefficient corresponding to various conditions. Representatives of such coefficient are intake air temperature correction coefficient corresponding to change in mass of the intake air due to change in intake air temperature, warming up correction coefficient for increasing the fuel injection quantity corresponding to the water temperature in order to accelerate warming up when the engine is started at a low temperature, feedback correction coefficient for increasing or decreasing the fuel injection quantity on the basis of oxygen information of the exhaust pipe in order to keep the air-fuel ratio at an appropriate value, and soon. Furthermore,correction coefficient for increasing the fuel quantity at the time of acceleration, correction coefficient for decreasing the fuel quantity at the time of deceleration and so on may be added, if necessary.
As a result, in the step S109, a calculated value according the driving time period Ting is calculated from at least the cooling water temperature, the intake air temperature, and intake air pressure.
As described above, in a predetermined time after starting at a high temperature, the fuel pressure acting on the fuel injection valve is increased. Therefore, reduction in fuel due to vapor, etc. is corrected in increasing tendency, whereby starting performance of the engine and stability in idling after starting are both improved.
However, in the conventional fuel injection control device of above construction and function, it is essential to include the fuel pressure switching solenoid 8 for switching the reference pressure regulated by the pressure regulator 4 from intake air pressure to atmospheric pressure. This results in a problem of increasing the cost.
Moreover, in the fuel pressure switching solenoid 8, the fuel pressure is increased by xcex94P corresponding to the pressure difference between the atmospheric pressure Pa and the intake air pressure Pb. Depending on the operating conditions, however, more or less fuel quantity than the pressure difference is actually increased in some cases. This results in a further problem of making it impossible to flexibly adjust the fuel quantity corresponding to the operating conditions.
The present invention was made to solve the above-discussed problems, and has an object of providing a fuel injection control device in which cost is low and fuel injection quantity is flexibly adjusted corresponding to the operating conditions.
A fuel injection control device according to the invention comprises:
a fuel injection valve for supplying a fuel into an intake pipe of an internal combustion engine,
a water temperature detector for detecting a cooling water temperature of the internal combustion engine,
an intake temperature detector for detecting an intake air temperature of the internal combustion engine,
a pressure detector for detecting an intake air pressure of the internal combustion engine,
means for deciding a driving time period for said fuel injection valve depending on a calculated value calculated from at least the cooling water temperature, the intake air temperature, and the intake air pressure, and
means for increasing the driving time period by multiplying the calculated value by a correction coefficient at a high temperature engine starting condition established corresponding to the cooling water temperature, the intake air temperature, and a progress time after starting time of the internal combustion engine,
wherein the high temperature engine starting condition is established on the condition that the cooling water temperature and the intake air temperature are higher than predetermined value, and the progress time is shorter than the predetermined value.
As a result of this, an advantage is achieved such that it is now possible to supply a deficient fuel quantity due to generation of vapor at the starting condition under starting engine at a high temperature, without any fuel pressure switching solenoid and, thus cost of the fuel injection control device is substantially reduced. Further, it is possible to flexibly establish the fuel injection quantity taking into consideration characteristics of individual engines and driving conditions thereof.